A human auditory system includes an outer ear, middle ear, and inner ear. With the outer ear, middle ear, and inner ear, the human auditory system is able to hear sound. The sound may come from various sound sources such as an audio speaker, people talking around the user, or vehicles passing by the user. A pinna of the outer ear receives the sound, directs the sound to an ear canal of the outer ear, which in turn directs the sound to the middle ear. The middle ear of the human auditory system transfers the sound into fluids of an inner ear for conversion into nerve impulses. A brain then interprets the nerve impulses to hear the sound. Further, the human auditory system is able to spatially localize the sound source. The perception is based on interactions with human anatomy. The interaction includes the sound reflecting, reverberating and/or diffracting off a head, shoulder and pinna. The interaction generates audio cues which are decoded by the brain to spatially localize the sound source.
It is now becoming more common to listen to sounds wearing personalized audio delivery devices such as headphones, headsets, hearables, earbuds, speakers, or hearing aids. The personalized audio delivery devices outputs sound, e.g., music, into the ear canal of the human auditory system. For example, a user wears an earcup seated on the pinna which outputs the sound into the ear canal of the human auditory system. Alternatively, a bone conduction headset vibrates middle ear bones to conduct the sound to the human auditory system. The user listens to the sound output by the personalized audio delivery device at the expense of usually not being able to spatially localize sound sources around the user. The sound does not interact with the human anatomy (e.g., pinna) when the user is wearing the personalized audio delivery device, audio cues are not generated, and as a result the person is not able to spatially localize the sound source.
A head related transfer function (HRTF) describes how a human head and ear shape modifies sound from a sound source at a given spatial location. The HRTF is typically determined by placing a microphone in an ear of a person and measuring how the sound from the sound source at the given spatial location is received at the microphone. In this regard, the HRTF indicates how the human head and/or ear modifies the sound. The HRTF is used to artificially generate the audio cues needed for the person to spatially localize the sound source even when the person is wearing a personalized audio delivery device.